The present invention relates to a method for cleaning clothes.
The dry cleaning technique is intended to remove soil from clothes by the use of a nonaqueous solvent, but conventional dry cleaning agents have the following three problems regarding environmental pollution. The first problem is based on the fact that all the organic solvents such as perchloroethylene, 1,1,1-trichloroethane and CFC 113 which have been widely used contain chlorine. Such chlorine containing solvents pollute the environment and destroy the ozone layer, and so, it will soon be impossible, by regulation, to use these solvents. The second problem is the waste pollution of detergents. Organic solvent can effectively remove hydrophobic soils, but the use of solvent alone cannot exert a sufficient cleaning ability. Nowadays, in order to improve the cleaning ability, a small amount of water and a soap (a surface active agent) for dry cleaning are added to the solvent. The used solvent is forcedly cleaned by a pressure filter, and at this time, the soil which has been removed from the clothes and dissolved in the solvent are removed together with powder adsorbing this soil.
The cleaned solvent is returned to the cleaning machine. Finally, the contaminated solvent is distilled, and the resulting residue is discharged. This residue is disposed of as an industrial waste, but since it contains the organic solvent and the surface active agent, its disposal is extremely difficult. The third problem is water pollution by the solvent caused by disposing water containing the solvent in the sewer system.
The present inventor has previously investigated the dry cleaning capabilities of 81 kinds of solvents [Journal of the Japan Research Association for Textile End-use, 27, 8, pp. 352-359 (1986)], but there has not been any solvent which can meet all requirements.
The solvent for dry cleaning must meet several requirements such as influence on the environment, detergency, handleability, safety, etc. Detergency is affected by the "solubility" and "dispersibility" of various types of soils, including oil-soluble soils such as skin oils, fat and oil, oil mist, etc.; water-soluble soils such as sweat, water-soluble foods, etc.; dirts such as sludge, dust, etc.; the degree of the "counter-contamination", or soils washed from clothes that migrate back from the cleaning liquid to the clothes; and the degree of surface tension of the solvent which penetrates into the clothes and between the soils. On the other hand, the "handleability" of the solvent is determined by the ease of drying the washed articles, the length of the solvent life, the pass of distillation and recovery of the solvent, suitability for machines with no corrosion of metal, its workability and management with low odor, no remaining odor in the washed articles, etc. Furthermore, the "safety" of the solvent is determined by the shape retention of the washed articles, denaturation of the washed articles including yellow discoloration, the decrease of gloss, the run-off of dye, the dissolution of auxiliary items such as buttons, cores and lames, as well as high ignition point and flash point, low toxicity, etc.
Propylene glycol monomethyl ether (hereinafter referred to as "PM") is known in the art as a detergent for home use (Japanese Unexamined Patent Publication No. 20400/1988), a detergent for floor use (Japanese Unexamined Patent Publication Nos. 112699/1988 and 168498/1988), a detergent for ink (Japanese Unexamined Patent Publication No. 73899/1990), and a letter-erasing liquid for erasing letters printed on clothes which is used together with a reducing or an oxidizing bleaching agent, but it is not yet known in the art that PM is used as a solvent for the dry cleaning of clothes.
The present invention is directed to a method which can solve all the problems of the above-mentioned conventional solvents, can completely achieve the inherent purpose of cleaning, and can prevent cleaning troubles.